Saddle gathering format is commonly used in collating multiple pages to create publications such as magazines and calendars. Saddle format means that an individual signature having a central fold line is placed on a moving line or gathering chain. Subsequent signatures each having a central fold line are placed in succession on top of the first signature with their central common fold lines lying together parallel and on top of the gathering line. The signatures are preprinted and their order of placement upon the gathering line is programmed so that upon binding the pages of the magazine or publication are in order. In the ordinary gathering line, the chain moves under the feeding devices. As it acquires more and more signatures, and upon emerging from the last feeding device it will have enough signatures compiled in the proper order to constitute a complete publication. Thereafter, a cover is generally applied and staples or another type of binding is added to hold the compiled signatures together.
Typically after stapling, the cover and the signatures are trimmed so that their margins register. Trimming is necessary because generally a small amount of inconsistencies exists along the edges of the various signatures after gathering.